With a linear analog to digital converter, the physical quantity variation corresponding to a variation of a least significant bit in the output digital word delivered by a digital to analog converter depends on the value of this digital word.
This is why a logarithmic analog to digital converter is preferentially used, in which this variation of a least significant bit may represent the same physical quantity variation regardless of the value of the digital word delivered as output from the converter.
There are numerous logarithmic analog to digital converter structures. Notable among these are the architectures that use an operational amplifier with a diode connected between the output and the negative input of this operational amplifier. Such devices do, however, have a strong dependency on the temperature and a very poor loop stability which leads to a limited conversion dynamic range.
Also worth citing are the analog to digital converters that use switched capacitance pipelined architectures. Such architectures are notably very complex to produce and have a high current consumption.